(i) 1 mole of $C_2H_6$ contains 2 moles of carbon atoms. Number of moles of carbon atoms in 3 moles of $C_2H_6$ = 3 × 2 = 6 (ii) 1 mole of $C_2H_6$ contains 6 moles of hydrogen atoms. Number of moles of hydrogen atoms in 3 moles of $C_2H_6$ = 3 × 6 = 18 (iii) 1 mole of $C_2H_6$ = 6.022 × $10^{23}$ molecules Number of molecules in 3 moles of $C_2H_6$ = 3 × 6.022 × $10^{23}$ = 1.807 × $10^{24}$ molecules